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Terahertz Photonics
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Terahertz Photonics

A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (15 December 2018) | Viewed by 87838

Special Issue Editor

Prof. Dr. Masayoshi Tonouchi

E-Mail Website
Guest Editor
Institute of Laser Engineering, Osaka University, Osaka 565-0871, Japan
Interests: teraherz propeties and physics; nanomaterials; terahertz microscopy; terahertz devices
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The Special Issue invites manuscripts that document the current state-of-the-art in Terahertz Photonics.

Terahertz science and technology, as defined as the frequency range of 0.3–30 THz, has attracted a great deal of interest owing to its potential applications. Nondestructive evaluation, bio/medical diagnosis, homeland security, and wireless communications are promising applications. Terahertz waves bridge electronics and photonics, as well as classical and quantum physics, where undeveloped research area locates. This Special Issue aims at highlighting all developments in the broad area of THz photonics. We will consider theoretical, numerical, and experimental papers that cover, but are not limited to, these topics:

(1) Advances in THz sources and detectors

(2) Progress in THz components, and sensing/imaging systems

(3) Novel THz devices and materials, such as ferroelectrics, superconductors, nanostructures, metamaterials, plasmonic materials and low- and two-dimensional materials

(4) Ultrafast carrier dynamics and THz nonlinear science, and new quantum physics in advance materials.

(5) THz applications:

  • industrial inspection, and non-destructive evaluation
  • defense and security
  • imaging and spectroscopy for bio/medical diagnostics,
  • information processing and computing
  • electronics/information/broadband communications

Prof. Dr. Masayoshi Tonouchi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (17 papers)

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Research

Jump to: Review

11 pages, 3198 KiB  
Article
300 GHz Optoelectronic Transmitter Combining Integrated Photonics and Electronic Multipliers for Wireless Communication
by Muhsin Ali, Jose Manuel Pérez-Escudero, Robinson-Cruzoe Guzmán-Martínez, Mu-Chieh Lo, Iñigo Ederra, Ramón Gonzalo, Luis Enrique García-Muñoz, Gabriel Santamaría, Daniel Segovia-Vargas, Frédéric van Dijk and Guillermo Carpintero
Photonics 2019, 6(2), 35; https://doi.org/10.3390/photonics6020035 - 27 Mar 2019
Cited by 9 | Viewed by 5793
Abstract
THz communications systems at carrier frequencies above 200 GHz are the key to enable next-generation mobile communication networks with 100 Gbit/s wireless data rates. One of the key questions is, which carrier frequency generation technique will be the most suitable. This is currently [...] Read more.
THz communications systems at carrier frequencies above 200 GHz are the key to enable next-generation mobile communication networks with 100 Gbit/s wireless data rates. One of the key questions is, which carrier frequency generation technique will be the most suitable. This is currently addressed by two separate approaches, electronics-based and photonics-based. We present in this paper a truly microwave photonic approach that benefits from the main key features of each, bandwidth, tunability, stability and fiber compatibility from photonics and power handling capability from the electronics. It is based on a Photonic Local Oscillator (PLO), generating a 100 GHz frequency, fed into an electronic frequency multiplier. A high speed uni-travelling carrier photodiode (UTC-PD) provides the 100 GHz PLO for Schottky tripler diodes, generating 300 GHz signal. To feed the UTC-PD, we present a photonic integrated mode locked laser source. According to the simulations and measurements, the developed transmitter can produce a maximum of 12 μW of THz power at 280 GHz. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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12 pages, 5224 KiB  
Article
Verification of Non-thermal Effects of 0.3–0.6 THz-Waves on Human Cultured Cells
by Noriko Yaekashiwa, Hisa Yoshida, Sato Otsuki, Shin’ichiro Hayashi and Kodo Kawase
Photonics 2019, 6(1), 33; https://doi.org/10.3390/photonics6010033 - 25 Mar 2019
Cited by 9 | Viewed by 4140
Abstract
Recent progress has been made in the development of terahertz (THz) waves for practical applications. Few studies that have assessed the biological effects of THz waves have been reported, and the data currently available regarding the safety of THz waves is inadequate. In [...] Read more.
Recent progress has been made in the development of terahertz (THz) waves for practical applications. Few studies that have assessed the biological effects of THz waves have been reported, and the data currently available regarding the safety of THz waves is inadequate. In this study, the effect of THz wave exposure on two cultured cells was assessed using a widely tunable THz source with a 0.3–0.6 THz frequency range, which can be used and increased in one GHz increments. The THz waves applied to the cultured cells were weak enough such that any thermal effects could be disregarded. The influence of THz wave exposure on both the proliferative and metabolic activities of these cells was investigated, as well as the extent of the thermal stress placed on the cells. In this work, no measurable effect on the proliferative or metabolic activities of either cell type was observed following the exposure to THz waves. No differences in the quantity of cDNA related to heat shock protein 70 was detected in either the sham or exposure group. As such, no differences in cellular activity between cells exposed to THz waves and those not exposed were observed. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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8 pages, 1218 KiB  
Article
A Novel Hexahedron Photonic Crystal Fiber in Terahertz Propagation: Design and Analysis
by Bikash Kumar Paul, Md. Ashraful Haque, Kawsar Ahmed and Shuvo Sen
Photonics 2019, 6(1), 32; https://doi.org/10.3390/photonics6010032 - 21 Mar 2019
Cited by 45 | Viewed by 4153
Abstract
A novel hexahedron fiber has been proposed for biomedical imaging applications and efficient guiding of terahertz radiation. A finite element method (FEM) has been applied to investigate the guiding properties rigorously. All numerically computational investigated results for optimum parameters have revealed the high [...] Read more.
A novel hexahedron fiber has been proposed for biomedical imaging applications and efficient guiding of terahertz radiation. A finite element method (FEM) has been applied to investigate the guiding properties rigorously. All numerically computational investigated results for optimum parameters have revealed the high numerical aperture (NA) of 0.52, high core power fraction of 64%, near zero flattened dispersion of 0.5 ± 0.6 ps/THz/cm over the 0.8–1.4 THz band and low losses with 80% of the bulk absorption material loss. In addition, the V–parameter is also inspected for checking the proposed fiber modality. The proposed single-mode hexahedron photonic crystal fiber (PCF) can be highly applicable for convenient broadband transmission and numerous applications in THz technology. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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13 pages, 1097 KiB  
Article
International System of Units (SI) Traceable Noise-Equivalent Power and Responsivity Characterization of Continuous Wave ErAs:InGaAs Photoconductive Terahertz Detectors
by Anuar de Jesus Fernandez Olvera, Axel Roggenbuck, Katja Dutzi, Nico Vieweg, Hong Lu, Arthur C. Gossard and Sascha Preu
Photonics 2019, 6(1), 15; https://doi.org/10.3390/photonics6010015 - 13 Feb 2019
Cited by 15 | Viewed by 4462
Abstract
A theoretical model for the responsivity and noise-equivalent power (NEP) of photoconductive antennas (PCAs) as coherent, homodyne THz detectors is presented. The model is validated by comparison to experimental values obtained for two ErAs:InGaAs PCAs. The responsivity and NEP were obtained from the [...] Read more.
A theoretical model for the responsivity and noise-equivalent power (NEP) of photoconductive antennas (PCAs) as coherent, homodyne THz detectors is presented. The model is validated by comparison to experimental values obtained for two ErAs:InGaAs PCAs. The responsivity and NEP were obtained from the measured rectified current, the current noise floor in the PCAs, and the incoming THz power for the same conditions. Since the THz power measurements are performed with a pyroelectric detector calibrated by the National Metrology Institute of Germany (PTB), the experimentally obtained values are directly traceable to the International System of Units (SI) for the described conditions. The agreement between the presented model and the experimental results is excellent using only one fitting parameter. A very low NEP of 1.8 fW/Hz at 188.8 GHz is obtained at room temperature. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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9 pages, 1637 KiB  
Article
A Terahertz-Microfluidic Chip with a Few Arrays of Asymmetric Meta-Atoms for the Ultra-Trace Sensing of Solutions
by Kazunori Serita, Hironaru Murakami, Iwao Kawayama and Masayoshi Tonouchi
Photonics 2019, 6(1), 12; https://doi.org/10.3390/photonics6010012 - 30 Jan 2019
Cited by 39 | Viewed by 6135
Abstract
Biosensing with terahertz (THz) waves has received large amounts of attention due to its potential to detect the functional expression of biomolecules in a label-free fashion. However, many practical challenges against the diffraction limit of THz waves and the strong absorption of THz [...] Read more.
Biosensing with terahertz (THz) waves has received large amounts of attention due to its potential to detect the functional expression of biomolecules in a label-free fashion. However, many practical challenges against the diffraction limit of THz waves and the strong absorption of THz waves into polar solvents still remain in the development of compact biosensors. Here, we present a non-linear, optical, crystal-based THz-microfluidic chip with a few arrays of asymmetric meta-atoms, an elementary unit of metamaterials, for the measurement of trace amounts of solution samples. A near-field THz emission source, that is locally generated in the process of optical rectification at a fs (femtosecond) laser irradiation spot, induces a sharp Fano resonance and modifies the resonance frequency of the meta-atoms when the channel is filled with solution samples of different concentrations. Using this chip, we successfully detected minute changes in the concentration of trace amounts of mineral water and aqueous sugar solutions by monitoring the shift in the resonance frequency. A higher detectable sensitivity of 1.4 fmol of solute in a 128 pL volume of solution was achieved. This was an improvement of one order of magnitude in the sensitivity compared to our previous experiment. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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8 pages, 1087 KiB  
Article
Nearly Single-Cycle Terahertz Pulse Generation in Aperiodically Poled Lithium Niobate
by Yuri Avetisyan and Masayoshi Tonouchi
Photonics 2019, 6(1), 9; https://doi.org/10.3390/photonics6010009 - 27 Jan 2019
Cited by 6 | Viewed by 3412
Abstract
In the present work, an opportunity of nearly single-cycle THz pulse generation in aperiodically poled lithium niobate (APPLN) crystal is studied. A radiating antenna model is used to simulate the THz generation from chirped APPLN crystal pumped by a sequence of femtosecond laser [...] Read more.
In the present work, an opportunity of nearly single-cycle THz pulse generation in aperiodically poled lithium niobate (APPLN) crystal is studied. A radiating antenna model is used to simulate the THz generation from chirped APPLN crystal pumped by a sequence of femtosecond laser pulses with chirped delays (m = 1, 2, 3 …) between adjacent pulses. It is shown that by appropriately choosing Δtm, it is possible to obtain temporal overlap of all THz pulses generated from positive (or negative) domains. This results in the formation of a nearly single-cycle THz pulse if the chirp rate of domain length δ in the crystal is sufficiently large. In the opposite case, a few cycle THz pulses are generated with the number of the cycles depending on δ. The closed-form expression for the THz pulse form is obtained. The peak THz electric field strength of 0.3 MV/cm is predicted for APPLN crystal pumped by a sequence of laser pulses with peak intensities of the separate pulse in the sequence of about 20 GW/cm2. By focusing the THz beam and increasing the pump power, the field strength can reach values in the order of few MV/cm. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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10 pages, 3484 KiB  
Article
Imaging of Chemical Reactions Using a Terahertz Chemical Microscope
by Toshihiko Kiwa, Tatsuki Kamiya, Taiga Morimoto, Kentaro Fujiwara, Yuki Maeno, Yuki Akiwa, Masahiro Iida, Taihei Kuroda, Kenji Sakai, Hidetoshi Nose, Masaki Kobayashi and Keiji Tsukada
Photonics 2019, 6(1), 10; https://doi.org/10.3390/photonics6010010 - 27 Jan 2019
Cited by 13 | Viewed by 3678
Abstract
This study develops a terahertz (THz) chemical microscope (TCM) that visualizes the distribution of chemical reaction on a silicon-based sensing chip. This chip, called the sensing plate, was fabricated by depositing Si thin films on a sapphire substrate and thermally oxidizing the [...] Read more.
This study develops a terahertz (THz) chemical microscope (TCM) that visualizes the distribution of chemical reaction on a silicon-based sensing chip. This chip, called the sensing plate, was fabricated by depositing Si thin films on a sapphire substrate and thermally oxidizing the Si film surface. The Si thin film of the sensing plate was irradiated from the substrate side by a femtosecond laser, generating THz pulses that were radiated into free space through the surface field effect of the Si thin film. The surface field responds to chemical reactions on the surface of the sensing plate, changing the amplitude of the THz pulses. This paper first demonstrates the principle and experimental setup of the TCM and performs the imaging and measurement of chemical reactions, including the reactions of bio-related materials. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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26 pages, 7761 KiB  
Article
THz Mixing with High-TC Hot Electron Bolometers: A Performance Modeling Assessment for Y-Ba-Cu-O Devices
by Romain Ladret, Annick Dégardin, Vishal Jagtap and Alain Kreisler
Photonics 2019, 6(1), 7; https://doi.org/10.3390/photonics6010007 - 25 Jan 2019
Cited by 7 | Viewed by 3989
Abstract
Hot electron bolometers (HEB) made from high-TC superconducting YBa2Cu3O7–x (YBCO) oxide nano-constrictions are promising THz mixers, due to their expected wide bandwidth, large mixing gain, and low intrinsic noise. The challenge for YBCO resides, [...] Read more.
Hot electron bolometers (HEB) made from high-TC superconducting YBa2Cu3O7–x (YBCO) oxide nano-constrictions are promising THz mixers, due to their expected wide bandwidth, large mixing gain, and low intrinsic noise. The challenge for YBCO resides, however, in the chemical reactivity of the material and the related aging effects. In this paper, we model and simulate the frequency dependent performance of YBCO HEBs operating as THz mixers. We recall first the main hypotheses of our hot spot model taking into account both the RF frequency effects in the YBCO superconducting transition and the nano-constriction impedance at THz frequencies. The predicted performance up to 4 THz is given in terms of double sideband noise temperature TDSB and conversion gain G. At 2.5 THz for instance, TDSB ≅ 1000 K and G ≅ − 6 dB could be achieved at 12.5 μW local oscillator power. We then consider a standoff target detection scheme and examine the feasibility with YBCO devices. For instance, detection at 3 m through cotton cloth in passive imaging mode could be readily achieved in moderate humidity conditions with 10 K resolution. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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8 pages, 2103 KiB  
Article
Bow-Tie Cavity for Terahertz Radiation
by Luigi Consolino, Annamaria Campa, Davide Mazzotti, Miriam Serena Vitiello, Paolo De Natale and Saverio Bartalini
Photonics 2019, 6(1), 1; https://doi.org/10.3390/photonics6010001 - 25 Dec 2018
Cited by 7 | Viewed by 5249
Abstract
We report on the development, testing, and performance analysis of a bow-tie resonant cavity for terahertz (THz) radiation, injected with a continuous-wave 2.55 THz quantum cascade laser. The bow-tie cavity employs a wire-grid polarizer as input/output coupler and a pair of copper spherical [...] Read more.
We report on the development, testing, and performance analysis of a bow-tie resonant cavity for terahertz (THz) radiation, injected with a continuous-wave 2.55 THz quantum cascade laser. The bow-tie cavity employs a wire-grid polarizer as input/output coupler and a pair of copper spherical mirrors coated with an unprotected 500 nm thick gold layer. The improvements with respect to previous setups have led to a measured finesse value F = 123, and a quality factor Q = 5.1·105. The resonator performances and the relevant parameters are theoretically predicted and discussed, and a comparison among simulated and experimental spectra is given. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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11 pages, 4362 KiB  
Article
Super-Oscillatory Metalens at Terahertz for Enhanced Focusing with Reduced Side Lobes
by Santiago Legaria, Victor Pacheco-Peña and Miguel Beruete
Photonics 2018, 5(4), 56; https://doi.org/10.3390/photonics5040056 - 05 Dec 2018
Cited by 13 | Viewed by 3848
Abstract
In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, efficiency is optimized, compared [...] Read more.
In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, efficiency is optimized, compared to the conventional transparent–opaque zoning approach that introduces, inevitably, a high reflection in the opaque regions. Furthermore, a novel two-step optimization technique, based on evolutionary algorithms, is developed to reduce the side lobes and boost the intensity at the focus. After the design process, we demonstrate that the metalens is able to generate a focal spot of 0.46λ0 (1.4 times below the resolution limit) at the design focal length of 10λ0 with reduced side lobes (the side lobe level being approximately −11 dB). The metalens is optimized at 0.327 THz, and has been validated with numerical simulations. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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12 pages, 2286 KiB  
Article
Absolute and Precise Terahertz-Wave Radar Based on an Amplitude-Modulated Resonant-Tunneling-Diode Oscillator
by Adrian Dobroiu, Ryotaka Wakasugi, Yusuke Shirakawa, Safumi Suzuki and Masahiro Asada
Photonics 2018, 5(4), 52; https://doi.org/10.3390/photonics5040052 - 27 Nov 2018
Cited by 30 | Viewed by 4363
Abstract
We present the principle of a terahertz-wave radar and its proof-of-concept experimental verification. The radar is based on a 522 GHz resonant-tunneling-diode oscillator, whose terahertz output power can be easily modulated by superimposing the modulation signal on its bias voltage. By using one [...] Read more.
We present the principle of a terahertz-wave radar and its proof-of-concept experimental verification. The radar is based on a 522 GHz resonant-tunneling-diode oscillator, whose terahertz output power can be easily modulated by superimposing the modulation signal on its bias voltage. By using one modulation frequency and measuring the time delay of the returning signal, a relative measurement of the propagation distance is possible; adding a second modulation frequency removes the ambiguity stemming from the periodicity of the modulation sine wave and allows an absolute distance measurement. We verified this measurement method experimentally and obtained a submillimeter precision, as predicted by theory. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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9 pages, 2056 KiB  
Article
A Highly Sensitive, Polarization Maintaining Photonic Crystal Fiber Sensor Operating in the THz Regime
by Sohel Rana, Nirmala Kandadai and Harish Subbaraman
Photonics 2018, 5(4), 40; https://doi.org/10.3390/photonics5040040 - 25 Oct 2018
Cited by 29 | Viewed by 4055
Abstract
In this paper, a high sensitivity, polarization preserving photonic crystal fiber (PCF), based on circular air holes for sensing in the terahertz (THz) band, is presented. The finite element method, a practical and precise computational technique for describing the interactions between light and [...] Read more.
In this paper, a high sensitivity, polarization preserving photonic crystal fiber (PCF), based on circular air holes for sensing in the terahertz (THz) band, is presented. The finite element method, a practical and precise computational technique for describing the interactions between light and matter, is used to compute the modal properties of the designed fiber. For the designed PCF, comprising of circular air holes in both the cladding and in the porous core, a relative sensitivity of 73.5% and a high birefringence of 0.013 are achieved at 1.6 THz. The all circular air-hole structure, owing to its simplicity and compatibility with the current fiber draw technique for PCF fabrication, can be realized practically. It is anticipated that the designed fiber can be employed in applications such as detection of biological samples and toxic chemicals, imaging, and spectroscopy. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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Review

Jump to: Research

20 pages, 6593 KiB  
Review
Surface Lattice Resonances in THz Metamaterials
by Thomas CaiWei Tan, Eric Plum and Ranjan Singh
Photonics 2019, 6(3), 75; https://doi.org/10.3390/photonics6030075 - 26 Jun 2019
Cited by 33 | Viewed by 7129
Abstract
Diffraction of light in periodic structures is observed in a variety of systems including atoms, solid state crystals, plasmonic structures, metamaterials, and photonic crystals. In metamaterials, lattice diffraction appears across microwave to optical frequencies due to collective Rayleigh scattering of periodically arranged structures. [...] Read more.
Diffraction of light in periodic structures is observed in a variety of systems including atoms, solid state crystals, plasmonic structures, metamaterials, and photonic crystals. In metamaterials, lattice diffraction appears across microwave to optical frequencies due to collective Rayleigh scattering of periodically arranged structures. Light waves diffracted by these periodic structures can be trapped along the metamaterial surface resulting in the excitation of surface lattice resonances, which are mediated by the structural eigenmodes of the metamaterial cavity. This has brought about fascinating opportunities such as lattice-induced transparency, strong nearfield confinement, and resonant field enhancement and line-narrowing of metamaterial structural resonances through lowering of radiative losses. In this review, we describe the mechanisms and implications of metamaterial-engineered surface lattice resonances and lattice-enhanced field confinement in terahertz metamaterials. These universal properties of surface lattice resonances in metamaterials have significant implications for the design of resonant metamaterials, including ultrasensitive sensors, lasers, and slow-light devices across the electromagnetic spectrum. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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27 pages, 5391 KiB  
Review
Terahertz Field Confinement in Nonlinear Metamaterials and Near-Field Imaging
by George R. Keiser and Pernille Klarskov
Photonics 2019, 6(1), 22; https://doi.org/10.3390/photonics6010022 - 28 Feb 2019
Cited by 21 | Viewed by 8476
Abstract
This article reviews recent advances in terahertz science and technology that rely on confining the energy of incident terahertz radiation to small, very sub-wavelength sized regions. We focus on two broad areas of application for such field confinement: metamaterial-based nonlinear terahertz devices and [...] Read more.
This article reviews recent advances in terahertz science and technology that rely on confining the energy of incident terahertz radiation to small, very sub-wavelength sized regions. We focus on two broad areas of application for such field confinement: metamaterial-based nonlinear terahertz devices and terahertz near-field microscopy and spectroscopy techniques. In particular, we focus on field confinement in: terahertz nonlinear absorbers, metamaterial enhanced nonlinear terahertz spectroscopy, and in sub-wavelength terahertz imaging systems. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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15 pages, 2858 KiB  
Review
Terahertz Polarization Imaging and Its Applications
by Shinichi Watanabe
Photonics 2018, 5(4), 58; https://doi.org/10.3390/photonics5040058 - 12 Dec 2018
Cited by 36 | Viewed by 6172
Abstract
This review focuses on several recent research activities regarding precise and fast polarization-sensitive terahertz time-domain spectroscopy systems for imaging purposes, and explains three interesting application examples. Owing to modulation techniques that have recently been developed for the evaluation of the instantaneous terahertz electric-field [...] Read more.
This review focuses on several recent research activities regarding precise and fast polarization-sensitive terahertz time-domain spectroscopy systems for imaging purposes, and explains three interesting application examples. Owing to modulation techniques that have recently been developed for the evaluation of the instantaneous terahertz electric-field (E-field) vector, fast and precise terahertz polarization imaging becomes feasible. This terahertz technology enables high-resolution surface topography, precise understanding of the spatial E-field vector distribution of the focused terahertz pulse, and examination of strain-induced birefringence in polymeric materials. These examples constitute a new application area of terahertz photonics with emphasis on both fundamental optics and industrial applications. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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12 pages, 1715 KiB  
Review
Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics
by Seiji Kojima
Photonics 2018, 5(4), 55; https://doi.org/10.3390/photonics5040055 - 03 Dec 2018
Cited by 6 | Viewed by 5023
Abstract
Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the [...] Read more.
Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the vicinity of the transverse and longitudinal optical mode frequencies. The significant frequency dependence enables valuable applications such as a tunable terahertz radiation source. The polariton dispersion relations of technologically important dielectric and ferroelectric crystals were reviewed in the broad terahertz range using terahertz time-domain spectroscopy, far-infrared spectroscopy, and Raman scattering spectroscopy. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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17 pages, 5619 KiB  
Review
Key Technologies for THz Wireless Link by Silicon CMOS Integrated Circuits
by Minoru Fujishima
Photonics 2018, 5(4), 50; https://doi.org/10.3390/photonics5040050 - 23 Nov 2018
Cited by 25 | Viewed by 5590
Abstract
In terahertz-band communication using ultra-high frequencies, compound semiconductors with superior high-frequency performance have been used for research to date. Terahertz communication using the 300 GHz band has nonetheless attracted attention based on the expectation that an unallocated frequency band exceeding 275 GHz can [...] Read more.
In terahertz-band communication using ultra-high frequencies, compound semiconductors with superior high-frequency performance have been used for research to date. Terahertz communication using the 300 GHz band has nonetheless attracted attention based on the expectation that an unallocated frequency band exceeding 275 GHz can be used for communication in the future. Research into wireless transceivers using BiCMOS integrated circuits with silicon germanium transistors and advanced miniaturized CMOS integrated circuits has increased in this 300 GHz band. In this paper, we will outline the terahertz communication technology using silicon integrated circuits available from mass production, and discuss its applications and future. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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